The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Air is drawn into an engine through an intake manifold. A throttle valve controls airflow into the engine. The air mixes with fuel from one or more fuel injectors to form an air/fuel mixture. The air/fuel mixture is combusted within one or more cylinders of the engine. Combustion of the air/fuel mixture generates torque.
Exhaust resulting from the combustion of the air/fuel mixture is expelled from the cylinders to an exhaust system. The exhaust may include particulate matter (PM) and gas. The exhaust gas includes nitrogen oxides (NOx), such as nitrogen oxide (NO) and nitrogen dioxide (NO2). A treatment system reduces NOx and oxidizes PM in the exhaust.
The exhaust flows from the engine to an oxidation catalyst (OC). The OC removes hydrocarbons and/or carbon oxides from the exhaust. The exhaust flows from the OC to a selective catalytic reduction (SCR) catalyst. A dosing agent injector injects a dosing agent into the exhaust stream, upstream of the SCR catalyst. Ammonia (NH3) provided by the dosing agent is absorbed by the SCR catalyst. Ammonia reacts with NOx in the exhaust passing the SCR catalyst.
A dosing module controls the mass flow rate of dosing agent injected by the dosing agent injector. In this manner, the dosing module controls the supply of ammonia to the SCR catalyst and the amount of ammonia stored by the SCR catalyst. The amount of ammonia stored by the SCR catalyst is referred to as current storage (e.g., grams). The percentage of NOx input to the SCR catalyst that is removed from the exhaust is referred to as the NOx conversion efficiency. The NOx conversion efficiency is related to the current storage of the SCR catalyst. For example, the NOx conversion efficiency increases as the current storage of the SCR catalyst increases and vice versa. The dosing module may control the injection of dosing agent, for example, to maximize the NOx conversion efficiency.